The compact disc can be used for storing a high density of digital data; the data are to be stored by means of a plurality of pits having different lengths and spaces along a spiral track around the center of the disc.
The compact disc usually includes a transparent substrate molded with a plurality of pits, a metallic coating on the substrate that can reflect the laser light, and a protective layer added as the surface. When reading out the data in a compact disc, a tiny laser in the player is focused on the spiral track from beneath while the compact disc is rotated at a constant linear velocity. The depth of the pits is equal to one half of the wave length of the laser (such as 0.1 mm). Since the pits and the plane portions (called lands) have a phase differential relation upon reflecting the laser beam, a different light contrast signal can be sensed corresponding to the length and space of the pits; that light contrast signal is then converted into an electronic signal, and decoded as on-off binary 1s and 0s (bits), which can be decoded, with a microprocessor, into the original data. The conventional laser recording method utilizes a photoresist layer deposited on a glass substrate. During the recording process, it is exposed by the laser beam which is modulated by the signal, then the pits are created during the development process of the photoresist layer, and then a silver film is coated thereon before the galvanic process needed for the manufacture of the pressing tools. The aforesaid manufacturing steps must be performed in a clean room environment, i.e., the manufacutring steps are cumbersome, and facilities therefore are expensive; as a result, the price of the laser disc is unable to be reduced.
The method of making the conventional record (LP) by using a diamond tool for the master has been used for making a CED video disc successfully. However, the quality of the LP is less than the laser video disc; for instance, the recorded data are analog signals, which when replayed have an inferior quality compared to digitally recorded signals. As a result, CED video disks were not manufactured in large quantity for commercial purpose.
In view of the aforesaid fact, an ideal and practical machine is necessary, which uses a diamond tool to cut pits directly on a master disc, so that the master disc make may be used directly, or used to duplicate compact discs in a mass production manner so as to lower the manufacturing cost, and to store the data thereon with digital signal to improve the quality of data. Since the recording pits on the compact disc are of high precision, the relationship between the cutting tool and the master disc and the moving speed thereof must be controlled accurately; therefore, a special control device is required to control the operation. In the conventional laser disc, the signal source for recording the master disc is from a PCM (pulse code modulation) tape machine, being played at a constant speed, which is unable to adapt to the characteristics of a machine using a tool to cut pits. Therefore, a special signal source means is required.
According to the aforesaid idea, the present invention has been developed to provide:
(1) a cutting machine which comprises a mechanical structure and a control device for executing an accurate operation between the cutting tool and the master disc; PA1 (2) a signal source for the cutting machine, of which the output signal speed can fit the characteristics of the cutting machine.